Some test scripts use ncat --sctp --listen port to run an SCTP discard server in the background.
However, when running in the background, stdin is closed and ncat initiates a graceful shutdown
of the SCTP association. This is not expected by the client.
Therefore, the ncat-based discard server is replaced by a perl-based one.
In addition, to remove the dependency from ncat, which needs to be installed via the nmap port, also the
code testing for a free SCTP port is changed to use the perl-based client.